How Unsharpen Tests How Far Pens Can Write

Updated

Unsharpen measures writing distance by pairing SVG test patterns with an Axidraw pen plotter — a drawing robot — so a pen can be run continuously under controlled, repeatable conditions until it stops writing. The method is documented on unsharpen.com under the post "Measuring How Far Pens Write: Writing Distance Test Pattern" (10/22/24), and it exists because claimed refill distances are large enough that human testing is impractical.

The core problem the test solves

Refill makers publish distance claims that are hard to verify by hand. Unsharpen cites the Fisher Space Pen PR4 refill as claiming up to 6,000 meters. Writing that much by hand would take an unreasonable amount of time and would introduce variation in pressure, speed, and paper contact. A plotter removes the human variable: it draws the same pattern at the same speed on the same paper, so the only thing changing between runs is the pen itself.

How the test works

Inputs

  • An SVG file containing the test pattern to be drawn.
  • An Axidraw pen plotter, which holds the pen and executes the SVG as physical strokes.
  • The pen being tested, mounted in the plotter.

Action

The plotter draws the SVG pattern repeatedly. Because the pattern is a defined file, each pass is identical in length and geometry, which means the total distance written is a known quantity that accumulates pass after pass.

Expected result

The pen keeps drawing until it runs out of ink or otherwise fails to mark the paper. The accumulated distance at that point is the measured writing distance for that pen.

Why the tests take so long

The bottleneck is the distance claims themselves. If a refill is rated near 6,000 meters, the plotter has to draw for a very long time to reach that figure — the article notes that even with a robot, the testing "can take a huge amount of time." This is a constraint of the subject matter, not the equipment: the robot removes human effort, but it cannot remove the raw distance a long-life refill is designed to cover.

What this means if you want to use the results

  • Comparisons are only fair within the same setup. Because the SVG pattern, plotter, and paper are fixed, differences in distance between pens reflect the pens, not the test conditions.
  • A single number is a stopping point, not a rating. The test measures how far a pen writes before it stops marking — it does not by itself tell you about line consistency, skipping, or how the last stretch of writing feels.
  • Long-life refills are the slow cases. Expect results for high-capacity refills to arrive later than results for pens that run dry quickly.

Unsharpen publishes these tests under its Pen Distance Testing category, alongside other data-driven pen and pencil articles such as "Which Pens Are Sold In The Most Sizes?" and "How Long Is A Pencil?"